RE: AII differences between PW routing and l2vpn signalling draft provisionong methods.

["Mustapha Aissaoui" <[e-mail]>]

Luca,
I do not believe there is any substantial difference that warrants to
standardize two different AII types. A MS-PW can also terminate on a VSI,
e.g., VPLS.

The issue is to be able to encode the target termination interface: an
endpoint for a p2p PW or a VSI for a VPLS in a way such that it will work
for both single hop PWs and MS-PWs. Both types can be used for the various
L2VPN applications.

Pragmatically, the way to go is to deprecate the FEC 129 as defined in
draft-ietf-l2vpn-signaling-06.txt (Type 1) and extend the Type 2 to cover
the various applications. One other reason to deprecate Type 1 is that we do
not want an implementation to use different FEC 129 types for single-hop PW
and MS-PW. FEC 128 will be restricted to singe hop PW and will be fine as
long as we specify a way to reach U-PEs which are on a FEC 129 Type 2
network.

Mustapha.
-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of
Luca Martini
Sent: Friday, December 02, 2005 1:09 PM
To: L2VPN
Cc: David McDysan; [e-mail]
Subject: AII differences between PW routing and l2vpn signalling draft
provisionong methods.

WG,

After a good discussion with Bruce Davie,  we came up with the following
explanation on why we need to have different AII type int he PW setup and
maintenance protocol.
This note explains why draft-ietf-l2vpn-signaling-06.txt (the L2VPN
Signaling draft) and draft-balus-bocci-martini-dyn-ms-pwe3-00.txt (the MS PW
draft) make use of different AII types, as defined in
draft-metz-aii-aggregate-01.txt.
 In a nutshell, the two drafts use different AII types because they are
tackling different problems. Specifically, L2VPN Signaling draft is
concerned with setting up all the PWs for a given L2VPN, while the MS PW
draft is concerned with setting up individual PWs.
 Because it is concerned with building L2VPNs, the L2VPN Signaling draft
makes use of the AGI (the contents of which effectively identify the
VPN) plus the AII to identify a particular PW. Hence, the AII only needs to
identify a "pool" or a VSI relative to a particular AGI. Hence a simple 32
bit AII is sufficient.
By contrast, because the MS PW draft is concerned with setting up individual
PWs, not L2VPNs, it has no use for the AGI - there is no "group" concept.
Hence it fully identifies the PW in the AII. Because there may be many PWs
connected to a given U-PE device, it is necessary to identify the PWs
relative to a given U-PE. And it is necessary to identify the U-PE within
the AII so that the signaling message can be routed toward the correct U-PE.
Hence the requirements for the AII are quite different, and it makes sense
to use an AII type that is designed to meet these requirements.
It is obvious that the simple AII type could be encoded in the more complex
AII type by leaving various fields set to zero, but this does not seem to
serve any useful purpose.

Luca